I have a Cocktail that I rescued two years ago. She is in with 6 other birds, also rescued. Of late she has plucked all the feathers off her neck and she looks like a rubber chicken. She has gotten aggressive with the other birds in a 7 ft flight cage. I have moved her to a cage of her own but the problem of no feathers is still there. Can anyone suggest a reason for this action and what I can do about it.